1. Field of the Invention
The present invention pertains to medical equipment, and more particularly, to a therapeutic ultrasound system for ablating obstructions within tubular anatomical structures such as blood vessels, and for myocardial revascularization of heart tissue.
2. Description of the Prior Art
A number of ultrasound systems and devices have heretofore been proposed for use in ablating or removing obstructive material from blood vessels. However, all of these systems and devices generally encounter three types of problems which are not always adequately addressed by these systems and devices.
The first type of problem relates generally to the effective transmission of ultrasound energy from an ultrasound source to the distal tip of the device where the ultrasound energy is applied to ablate or remove obstructive material. Since the ultrasound source, such as a transducer, is usually located outside the human body, it is necessary to deliver the ultrasound energy over a long distance, such as about 150 cm, along an ultrasound transmission wire from the source to the distal tip. Attenuation of the acoustical energy along the length of the transmission wire means that the energy reaching the distal tip is reduced. To ensure that sufficient energy reaches the distal tip, a greater amount of energy must be delivered along the transmission wire from the source to the distal tip. This transmission of increased energy along the transmission wire may increase the fatigue experienced by the transmission wire at certain critical locations, such as at the connection between the transducer and the transmission wire.
The second type of problem relates to the need for accurately positioning the ultrasound device inside a patient's vasculature, and in particular, where the vasculature contains smaller and more tortuous vessels. To address this need, flexible and low-profile ultrasound devices have been provided which allow the device to be navigated through small and tortuous vessels. To provide a more flexible ultrasound transmission wire for such flexible and low-profile ultrasound devices, the cross-sectional area of the transmission wire is usually tapered or narrowed near the distal end. While such tapering or narrowing decreases rigidity and improves bendability, it causes a significant increase in amplitude of the ultrasound energy being transmitted through the tapered or narrowed region, thereby increasing the likelihood of breakage or fracture of the transmission wire due to the increased transverse motion. These transverse micro-motions are produced by the transducer and further amplified by any tapering or narrowing of the transmission wire.
The third type of problem relates to the application of undesirable external forces to the connection between the transducer and the transmission wire during clinical use of the ultrasound device. Such forces may be applied during the bending, pushing, torquing and pressing of the ultrasound device as the device is being introduced and navigated along the patient's vasculature. These forces may result in the overloading of the transducer, which may minimize the amount of ultrasound energy delivered to the distal end of the catheter device 10. These forces may also increase transducer output to compensate for this unwanted load, which may result in transducer overheating and hardware failure.
The above-described problems are similarly experienced by ultrasound systems where ultrasound energy is used to percuataneously revascularize the myocardium of the heart.
Thus, there still exists a need in the art for improved ultrasound systems having ultrasound devices or catheters which address the aforementioned problems. In particular, there is a need for ultrasound devices that: (1) are sufficiently flexible to be inserted into and advanced along both small and tortuous blood vessels, (2) provide an improved connection between the transmission member and the transducer, (3) provide an improved ultrasound transmission member which combines strength, elasticity and effective transmission properties, (4) provide improved configurations for the distal end that are effective in ablating or removing occlusive material in vessels, and (5) mitigate the impact of undesirable loading on the connection between the transmission member and the transducer.